This command disables the engine's deferred compute shader lighting path. This may give a large FPS boost in open, outdoor areas, but possibly may reduce performance in heavily lit scenes. Most users report only the performance boost, including inside closed areas.

On Processor power management change the maximum cpu usage to 99% instead of 100%. This will disable TurboBoost, which is the reason for weird performance issues in connection with Battlefield 3.

ATTENTION: You might also have to turn down minimum CPU usage if it is set to 100% (eg Max performance mode often has this). Also your performance will get steadier with both minimum and maximum settings set to 99%, but at the cost of battery life.

You can have these commands run automatically, whenever you start the game, by entering them in user.cfg in the Battlefield 3 installation folder (the file won't exist by default, you can create it through Notepad and save as a .cfg file).